1. Field of the Invention
This invention relates to novel quaternary ammonium trihalides soluble in organic solvent and a method for the dissolution of metal which is useful for the extraction and recovery of the metal.
2. Description of the Prior Art
The dissolution of a metal is an indispensable step in the extraction and recovery of the metal from a mixture in which it is contained and, as such, is highly important from the industrial point of view. The conventional method used for this dissolution has been to dissolve the metal in an aqueous solution of an inorganic acid such as hydrochloric acid.
The conventional method of dissolution by use of an inorganic acid is dangerous to conduct because of the need to use a strongly acidic aqueous solution. Moreover, it generates a large volume of waste water that requires expensive processing for disposal.
With a view to overcoming such drawbacks of the prior art described above, the present inventors earlier conducted various studies in search of a method for effecting the dissolution of metals without use of any inorganic acid and consequently developed a method for the dissolution of metals by contacting the metal with a halogenated hydrocarbon in the presence of a surfactant. They were granted U.S. Pat. No. 4,919,716 on this invention.
This method, however, has a problem in that since the surfactant has a large molecular weight, the consumption thereof necessary for the dissolution amounts to a large number of grams.
Through further studies the inventors learned that many metals are dissolved when they are brought into contact with a quarternary ammonium compound and a halogenated hydrocarbon optionally, further with a polar solvent. This invention was filed for paten under U.S. Application Ser. No. 07/603,438 dated Oct. 26, 1990, now U.S. Pat. No. 5,120,523.
Though this method provides highly satisfactory dissolution for various metals, it still falls short of satisfying the practical need for the dissolution to be effected quickly with high efficiency. All of the methods mentioned so far exhibit poor efficiency in the dissolution of gold.
In view of the problems of the earlier methods, the inventors conducted a study for the purpose of developing a method for the dissolution of metal which is capable of easily dissolving metals including gold under moderate conditions as compared with the conventional methods described above. As a result, they learned that novel quarternary ammonium trihalides are produced by the reaction of a cationic surfactant with an elemental halogen and that numerous metals are easily dissolved by contact with an organic solvent in the presence of these quarternary ammonium trihalides. The present invention has been completed as a result.